1. Field of the Invention
This invention relates to a scroll type compressor for use in vehicle air conditioning system, general refrigeration air conditioning system, heat pump, air compressor and the like.
2. Description of the Prior Art
A conventional scroll type compressor of the first type has been proposed in, for example, Japanese Patent Unexamined Publication (JP-A) No. 8-49670 (1996).
In this scroll type compressor, a first housing in which a bottom plate and a scroll portion are integrally formed and which acts also as a fixed scroll member and a second housing accommodating a movable scroll member having a bottom plate and a scroll portion are engaged with each other at their scroll portions so as to form a compression chamber in both housings. By revolving the movable scroll member around an axis of the fixed scroll member, the compression chamber is moved from their peripheral walls to a center portion so as to compress gas. Sectional shape of each of both housings is nearly elliptic.
A conventional scroll type compressor of the second type will be described with reference to FIGS. 1 and 2.
A fixed scroll member 11 is formed integrally with a disc-like bottom plate 12 and a movable scroll member 14 is formed integrally with a bottom plate 15. The movable scroll member 14 is engaged with the fixed scroll member 11 so that it is capable of circulating under a predetermined circulation radius R.sub.0. A discharge hole 13 is provided in a center of the disc-like bottom plate 12.
An Oldham coupling will be described with reference to FIG. 2. A bottom plate 15 formed integrally with the movable scroll member 14 has key grooves 15a, 15a on both sides in the X-axis direction. A boss 15b is provided at an eccentric position such that a bearing is fit thereto. An Oldham ring 16 has keys 16a, 16a on both sides in the X-axis direction and has keys 16b, 16b in the Y-axis direction. A housing 17 has key grooves 17a, 17a on both sides in the Y-axis direction.
The keys 16a, 16a of the Oldham ring 16 are fit to the key grooves 15a, 15a of the bottom plate 15 and the keys 16b, 16b of the Oldham ring 16 are fit to the key grooves 17a, 17a of the housing 17. Therefore, the movable scroll member 14 is capable of moving both in the X-axis and Y-axis directions relative to the housing 17.
In FIG. 1B, if the Oldham ring 16 reciprocates in the Y-axis direction, the movable scroll member 14 is prevented from its rotation by the Oldham coupling, so that it is driven along a circulation orbit of a perfect circle. FIGS. 1C and 1D show respectively a status after a phase of each of the movable scroll member 14 and the Oldham ring 16 is changed. Incidentally, the length of the arm of the Oldham ring 16 is assumed to be A.
Due to a reciprocation of the Oldham ring 16, a centrifugal force changes during one rotation of the movable scroll member 14, thereby producing a vibration. If a total mass of a movable scroll member 14 and parts circulating together therewith is ma and a mass of the Oldham ring 16 is mb, a circulation radius of the movable scroll member 14 is R.sub.0 and an angular speed of the movable scroll member 14 is .omega., a component F.sub.Y in the Y-axis direction of a centrifugal resultant force .SIGMA.F and a component F.sub.X in the X-axis direction of the same are expressed by the following formulae, EQU F.sub.Y =(ma+mb)R.sub.0 .omega..sup.2 EQU F.sub.X =maR.sub.0 .omega..sup.2
In the aforementioned conventional scroll type compressor of the first type, since the movable scroll member moves along an elliptic circulating orbit, the centrifugal force changes depending on a position of the volute (phase angle), so that vibration and noise are generated. Further, since major parts of the compressor such as the movable scroll member, the fixed scroll member, the housing and the like are all formed in the shape based on an ellipse, they cannot be processed easily by cutting work by means of a lathe. Therefore, the production cost is high.
In the aforementioned conventional scroll type compressor of the second type, vibration and noise are generated by the reciprocation of the Oldham ring.